7.2 Enzymes and Their Characteristics

Short Introduction generated by DeepSeek to PDF

Vital biochemical reactions taking place in the body must occur quickly and precisely for a cell to perform and survive. These metabolic reactions in living organisms are sped up by specific proteins in the body called biological catalysts or enzymes. Enzymes are biologically active globular proteins made by living cells, which tremendously speed up biochemical reactions.

Main Idea

Enzymes are biological catalysts — mostly proteins — that speed up biochemical reactions without being consumed. They act on specific molecules called substrates, converting them into products. Enzymes have several key characteristics: they are globular proteins, required in small quantities, highly specific, often require cofactors, can be regulated, form metabolic pathways, and lower the activation energy of reactions.

Core Concept

Definition of Enzymes "Enzymes are biologically active globular proteins made by living cells, which tremendously speed up the biochemical reactions." Each cell synthesizes its own enzymes. The type of enzymes produced in each cell is specific, determined by the genes active in that cell. Substrates and Products Enzymes act on specific molecules in the cell called substrates. The substrates are the molecules entering into chemical reactions. After binding to their specific enzyme, substrates undergo chemical changes resulting in a new bonding arrangement. The substrates modified by enzymes are called products. Intracellular and Extracellular Enzymes Intracellular enzymes: Enzymes that stay inside the cells to speed up reactions (e.g., enzymes of glycolysis working in the cytoplasm). Extracellular enzymes: Enzymes made inside the cells that are allowed to go out of the cell to do their work outside (e.g., pepsin enzyme working in the stomach cavity). Fungi and bacteria release extracellular enzymes to digest their food. Enzymology: The study of the structure, type, and role of enzymes. Characteristics of Enzymes 1. Enzymes are Globular Proteins All enzymes are made up of chains of amino acids folded to form 3D protein molecules called globular proteins. Few enzymes are RNA in nature called ribozymes. 2. Enzymes Increase the Rate of Reaction Reactions may initiate without enzymes, but it would be extremely slow and may take months or years. Enzymes speed up reactions millions of times faster than non-enzymatic reactions. Important: Enzymes only speed up a reaction and do not start a chemical reaction. 3. Enzymes are Required in Small Quantity Structure of enzymes may slightly change during a reaction but they regain their actual shape, so they remain unchanged at the end of the reaction. generated by DeepSeek to PDF

They can be used repeatedly. Thus, a very small quantity of an enzyme is capable of catalysing a huge amount of substrate. 4. Enzymes are Specific Enzymes are usually very specific, so they catalyse only one type of reaction and will not act on a different substrate. For example, amylase will only act on starch and not on proteins or fats. 5. Enzymes Require Co-factor Many enzymes require an additional non-protein component for their proper functioning called a cofactor. Cofactors usually act as a bridge between the protein part of the enzyme and its substrate or may provide energy to the enzyme. Three types of cofactors: a. Activator: Some enzymes require detachable inorganic ions as cofactors called activators, such as Zn⁺, Fe⁺, Cu⁺, and chlorides. For example, the activity of salivary amylase is increased in the presence of chloride ions. b. Prosthetic group: If the cofactor is an organic molecule tightly and permanently attached to the enzyme, it is known as a prosthetic group. For example, Flavin Adenine Dinucleotide (FAD), Haem group. c. Coenzyme: If the cofactor is a detachable organic molecule, it is called a coenzyme. Examples include NAD (nicotinamide adenine dinucleotide), coenzyme A, and vitamins A and C. 6. Regulation of Enzyme Production and Activity Synthesis of enzymes within the cells can be increased or decreased by a cell according to requirements. Enzyme activity can be regulated by inhibitors or activators within or from outside the cell. 7. Enzymes Make Metabolic Pathways Many enzymes work together in a specific sequence to make metabolic pathways. A metabolic pathway is a series of connected chemical reactions where multiple intermediate molecules are produced before conversion of an initial substrate into a final product. 8. Energy of Activation The minimum amount of extra energy required to activate the molecule to react or start the reaction is called the energy of activation. Enzymes lower the activation energy so that these reactions can take place at body temperature. Enzymes lower the activation energy by changing the shape and charge of the substrate, or by providing an entirely different mechanism of reaction.

Detailed Explanation

Enzymes are the molecular machines that drive the chemistry of life. They are essential for almost every biological process. 1. Globular Proteins: Most enzymes are globular proteins with a specific three-dimensional shape. This shape is critical for their function because it creates a specific active site where the substrate binds. A few enzymes are RNA molecules called ribozymes. generated by DeepSeek to PDF

2. Catalytic Efficiency: Enzymes are incredibly efficient. They can speed up reactions by factors of millions or more. Without enzymes, the biochemical reactions in our body would be far too slow to sustain life. However, it's important to remember that enzymes do not start reactions; they only accelerate them. 3. Reusability: Because enzymes are not consumed in the reaction, they can be used over and over again. A single enzyme molecule can catalyze thousands of substrate molecules per second. This explains why enzymes are required in such small quantities. 4. Specificity: Enzymes are highly specific. The active site of an enzyme has a shape and charge distribution that complements only one specific substrate (or a group of closely related substrates). This is often described as the "lock and key" or "induced fit" model. For example, amylase only breaks down starch; it cannot break down proteins or fats. 5. Cofactors: Many enzymes need "helpers" called cofactors to function. These can be: Activators: Inorganic ions (e.g., Zn⁺, Fe⁺, Cu⁺, Cl⁻) that help the enzyme work. For example, chloride ions activate salivary amylase. Prosthetic groups: Organic molecules tightly bound to the enzyme (e.g., FAD, haem). Coenzymes: Organic molecules that are loosely bound and can detach (e.g., NAD, coenzyme A, vitamins A and C). 6. Regulation: Enzyme activity is carefully regulated. Cells can produce more or less enzyme depending on need. Enzyme activity can also be inhibited or activated by molecules inside or outside the cell. 7. Metabolic Pathways: Enzymes often work in teams, forming metabolic pathways. In a pathway, the product of one enzyme-catalyzed reaction becomes the substrate for the next enzyme. This allows complex molecules to be built or broken down in a controlled, step-by-step manner. 8. Activation Energy: Every chemical reaction requires an initial input of energy to get started, called the activation energy. Enzymes lower this energy barrier, making it easier for the reaction to occur at the body's normal temperature. They do this by bringing substrates together in the correct orientation, straining bonds, or providing an alternative reaction pathway.

Intermediate Level

• Globular proteins: Most are proteins; some are RNA (ribozymes).
• Increase reaction rate: They speed up reactions millions of times but do not start them.
• Required in small quantities: They are reusable and remain unchanged after the reaction.
• Specific: They catalyze only one type of reaction (e.g., amylase acts only on starch).

• Require cofactors: Cofactors can be activators (inorganic ions like Zn⁺, Cl⁻), prosthetic groups (tightly
• Regulated: Enzyme production and activity can be increased or decreased as needed.
• Form metabolic pathways: Many enzymes work in sequence to convert a substrate through
• Lower activation energy: They reduce the energy required to start a reaction, enabling reactions to

Important Points

• 1. Enzymes are biologically active globular proteins made by living cells that speed up biochemical
• reactions.
• 2. Each cell synthesizes its own enzymes; the type is determined by active genes.
• 3. Substrates are the molecules entering into chemical reactions.
• 4. Products are the substrates modified by enzymes.
• 5. Intracellular enzymes stay inside cells (e.g., glycolysis enzymes in cytoplasm).
• 6. Extracellular enzymes are released outside the cell (e.g., pepsin in the stomach).
• 7. Enzymology = study of enzymes.
• 8. Characteristics of enzymes:
• Globular proteins (few are RNA = ribozymes).
• Increase the rate of reaction (millions of times faster; do not start reactions).
• Required in small quantity (reusable; unchanged at the end).
• Specific (e.g., amylase only acts on starch).
• Require cofactors:
• Activators: Inorganic ions (Zn⁺, Fe⁺, Cu⁺, chlorides). Example: chloride ions increase
• salivary amylase activity.
• generated by DeepSeek to PDF
• Prosthetic group: Tightly bound organic molecule (e.g., FAD, haem).
• Coenzyme: Detachable organic molecule (e.g., NAD, coenzyme A, vitamins A and C).
• Regulation of enzyme production and activity (increased/decreased by cell; regulated by
• inhibitors/activators).
• Enzymes make metabolic pathways (series of connected reactions with intermediate
• molecules).
• Energy of activation: The minimum extra energy required to start a reaction. Enzymes lower it
• so reactions can take place at body temperature.

Remember

• Enzymes = biological catalysts (globular proteins; few RNA = ribozymes).
• Speed up reactions (millions of times faster; do not start).
• Reusable in small quantities.
• Specific (amylase → starch only).
• Cofactors:
• Activators = inorganic ions (Zn⁺, Cl⁻).
• Prosthetic group = tightly bound organic (FAD, haem).
• Coenzyme = detachable organic (NAD, coenzyme A, vitamins A and C).
• Metabolic pathways = enzymes working in sequence.
• Activation energy = minimum extra energy to start a reaction; enzymes lower it.

Common Mistakes

• 1. Thinking enzymes start reactions: Enzymes only speed up reactions; they do not start them.
• 2. Thinking enzymes are consumed: Enzymes remain unchanged at the end and can be reused.
• 3. Forgetting that enzymes are specific: Each enzyme acts on a specific substrate (e.g., amylase only on
• starch).
• 4. Confusing activators, prosthetic groups, and coenzymes: Activators are inorganic ions; prosthetic
• groups are tightly bound organic molecules; coenzymes are loosely bound organic molecules.
• 5. Thinking all enzymes are proteins: Most are, but some are RNA (ribozymes).
• 6. Forgetting that enzymes lower activation energy: They reduce the energy needed to start a reaction,
• allowing it to occur at body temperature.
• 7. Thinking extracellular enzymes work inside the cell: Extracellular enzymes are released outside the cell
• (e.g., pepsin in the stomach).

Quick Revision

• Enzymes are biological catalysts, mostly globular proteins, that speed up biochemical reactions without being
• consumed. They act on specific substrates and convert them into products. Key characteristics include: they are
• globular proteins (some are RNA ribozymes); they increase reaction rates millions of times but do not start
• reactions; they are required in small quantities and are reusable; they are specific (e.g., amylase only acts on starch);
• they require cofactors (activators, prosthetic groups, or coenzymes); their production and activity are regulated; they
• form metabolic pathways; and they lower the activation energy of reactions, enabling them to occur at body
• temperature. Enzymes may be intracellular (inside cells) or extracellular (released outside cells).

60-Second Revision

• Enzymes = biological catalysts (globular proteins; few RNA = ribozymes).
• Speed up reactions (millions of times faster; do not start).
• Reusable in small quantities.
• Specific (amylase → starch only).
• Cofactors:
• Activators = inorganic ions (Zn⁺, Cl⁻).
• Prosthetic group = tightly bound organic (FAD, haem).
• Coenzyme = detachable organic (NAD, coenzyme A, vitamins A and C).
• Metabolic pathways = enzymes working in sequence.
• Activation energy = minimum extra energy to start a reaction; enzymes lower it.
• Frequently Asked Questions (FAQs)
• Q1. What are enzymes? Answer: Enzymes are biologically active globular proteins made by living cells, which
• tremendously speed up biochemical reactions. They are biological catalysts.
• Q2. What are substrates and products? Answer: Substrates are the molecules entering into chemical reactions that
• bind to enzymes. Products are the substrates modified by enzymes after the reaction.
• Q3. What is the difference between intracellular and extracellular enzymes? Answer: Intracellular enzymes stay
• inside the cells to speed up reactions (e.g., enzymes of glycolysis in the cytoplasm). Extracellular enzymes are made
• inside the cells but are allowed to go out of the cell to do their work outside (e.g., pepsin in the stomach cavity).
• Q4. What are the characteristics of enzymes? Answer: The characteristics of enzymes are:
• 1. Enzymes are globular proteins (few are RNA called ribozymes).
• 2. Enzymes increase the rate of reaction (millions of times faster, but do not start reactions).
• 3. Enzymes are required in small quantities (they are reusable).
• 4. Enzymes are specific (e.g., amylase only acts on starch).
• 5. Enzymes require cofactors.
• 6. Regulation of enzyme production and activity.
• 7. Enzymes make metabolic pathways.
• 8. Enzymes lower the energy of activation.
• Q5. What is a cofactor? What are its types? Answer: A cofactor is an additional non-protein component required
• by many enzymes for proper functioning. It acts as a bridge between the enzyme and its substrate or provides
• energy. There are three types:
• generated by DeepSeek to PDF

• 1. Activator: Detachable inorganic ions (e.g., Zn⁺, Fe⁺, Cu⁺, chlorides). Example: chloride ions increase
• salivary amylase activity.
• 2. Prosthetic group: An organic molecule tightly and permanently attached to the enzyme (e.g., FAD, haem
• group).
• 3. Coenzyme: A detachable organic molecule (e.g., NAD, coenzyme A, vitamins A and C).
• Q6. What is a metabolic pathway? Answer: A metabolic pathway is a series of connected chemical reactions where
• multiple intermediate molecules are produced before conversion of an initial substrate into a final product. Many
• enzymes work together in a specific sequence to make metabolic pathways.
• Q7. What is the energy of activation? How do enzymes affect it? Answer: The energy of activation is the
• minimum amount of extra energy required to activate the molecule to react or start the reaction. Enzymes lower the
• activation energy so that reactions can take place at body temperature. They do this by changing the shape and
• charge of the substrate or by providing an entirely different mechanism of reaction.
• Q8. What are ribozymes? Answer: Ribozymes are a few enzymes that are RNA in nature.
• Q9. What is enzymology? Answer: Enzymology is the study of the structure, type, and role of enzymes.
• Q10. Give an example of enzyme specificity. Answer: Amylase will only act on starch and not on proteins or fats.
• This shows that enzymes are specific.
• Multiple Choice Questions (MCQs)
• Q1. Enzymes are: A. Carbohydrates B. Lipids C. Globular proteins D. Nucleic acids Correct Answer: C Explanation:
• Enzymes are biologically active globular proteins (few are RNA).
• Q2. Which of the following is NOT a characteristic of enzymes? A. They increase the rate of reaction B. They are
• required in large quantities C. They are specific D. They lower activation energy Correct Answer: B Explanation:
• Enzymes are required in small quantities because they are reusable.
• Q3. The molecules on which enzymes act are called: A. Products B. Substrates C. Cofactors D. Activators Correct
• Answer: B Explanation: Substrates are the molecules entering into chemical reactions that bind to enzymes.
• Q4. Which of the following is an example of an intracellular enzyme? A. Pepsin B. Glycolysis enzymes C. Amylase in
• saliva D. Trypsin Correct Answer: B Explanation: Glycolysis enzymes work in the cytoplasm (intracellular). Pepsin,
• salivary amylase, and trypsin are extracellular.
• Q5. Enzymes that are RNA in nature are called: A. Ribozymes B. Coenzymes C. Prosthetic groups D. Activators
• Correct Answer: A Explanation: Few enzymes are RNA in nature called ribozymes.
• Q6. The activity of salivary amylase is increased by the presence of: A. Zinc ions B. Iron ions C. Chloride ions D.
• Copper ions Correct Answer: C Explanation: The activity of salivary amylase is increased in the presence of chloride
• ions.
• Q7. A tightly and permanently attached organic cofactor is called a: A. Coenzyme B. Activator C. Prosthetic group D.
• Substrate Correct Answer: C Explanation: A prosthetic group is an organic molecule tightly and permanently
• attached to the enzyme.
• Q8. NAD and coenzyme A are examples of: A. Prosthetic groups B. Coenzymes C. Activators D. Substrates Correct
• Answer: B Explanation: NAD and coenzyme A are coenzymes (detachable organic molecules).
• generated by DeepSeek to PDF

• Q9. The minimum amount of extra energy required to start a reaction is called: A. Free energy B. Activation energy
• C. Kinetic energy D. Potential energy Correct Answer: B Explanation: The energy of activation is the minimum extra
• energy required to start a reaction.
• Q10. A series of connected chemical reactions where multiple intermediate molecules are produced is called a: A.
• Metabolic pathway B. Reaction chain C. Cofactor cycle D. Enzyme complex Correct Answer: A Explanation: A
• metabolic pathway is a series of connected chemical reactions with intermediate molecules.
• Subtopic 7.2 complete. Reply "next" to approve and I will produce Subtopic 3: 7.3 Mechanism of Enzyme
• Action.